In manufacturing semiconductor devices, a circuit pattern is transferred onto a photo-resist, using a photo lithography technique, and the photo-resist is subjected to a developing process. Where a photo lithography technique is used, it is necessary to perform, for example, a hydrophoby-providing step, resist coating step, developing step, baking step, cleaning step, etc.
As a baking step, there is a pre-baking step and a post-baking step. The pre-baking step is performed to heat and vaporize residual solvent in a resist applied on a semiconductor wafer, thereby baking and curing the resist. The post-baking step is performed to heat and vaporize residual developing solution in the resist after it is developed.
In a semiconductor processing system for performing a photo lithography technique, a plurality of process apparatuses for performing respective steps are integrated and combined to improve the operating efficiency. Heat-processing means for baking (heating means) is formed of pre-baking units and post-baking units stacked one on the other (for example, Jpn. Pat. Appln. KOKAI Publication No. 8-274015). One heat-processing unit may be commonly used for pre-baking and post-baking.
A heat-processing apparatus of this kind includes a hot plate formed of, e.g., a ceramic plate of SiC or the like with resistance heating wires built therein. On the hot plate, a semiconductor wafer having a top surface coated with a resist film is placed. Then, the semiconductor wafer is kept at e.g., about 150° C. for a predetermined time to bake and cure the resist film.
In order to ensure high accuracy in the thickness of the resist film and planar uniformity thereof, it is necessary to control temperature in heating the semiconductor wafer and planar uniformity thereof with high accuracy. For this reason, the hot plate described above is prepared to have a plurality of, e.g., ten-odd, heating zones planarly arrayed, in which thermo couples are respectively disposed. On the basis of the temperature detected by the thermo couples, heaters are independently controlled for respective heating zones.
However, where the hot plate includes a number of heating zones thus divided, which are controlled for temperature with high accuracy, a very complex structure is required, which increases the cost. Further, this complex structure remarkably increases the weight of the apparatus.
As another heat-processing apparatus, there is one in which a heating gas flows on the opposite sides of a semiconductor wafer, while the semiconductor wafer is floated by the gas (for example, Jpn. Pat. Appln. KOKAI Publication No. 2000-091249). However, in this apparatus, the heating gas blown onto a resist film affects the thickness of the resist film and planar uniformity of the thickness.
The problems described above are becoming more serious in recent years, as the wafer size increases from 200 mm to 300 mm, line width is further miniaturized, and film thickness is reduced.